Applicants claim, under 35 U.S.C. xc2xa7119, the benefit of priority of the filing date of Jul. 31, 2001 of a German patent application, copy attached, Serial Number 101 37 493.3, filed on the aforementioned date, the entire contents of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a method for producing a self-supporting electron-optical transparent structure, composed of strips of several layers and recesses located between the strips. The present invention also relates to a structure produced in accordance with the method.
2. Discussion of Related Art
Electron-optical transparent structures are employed for example as absorbing structures, often also called masks, in electron-beam lithography. For example, periodically repeated patterns (xe2x80x9ccell projectionxe2x80x9d), or patterns of variable size (xe2x80x9cvariable shaped beamxe2x80x9d), are projected by means of these structures, which are capable of beam absorption, on substrates appropriately coated with light-sensitive materials, which in the end can be used as patterns for wafer steppers in the semiconductor industry, or as scale graduations. In the process, electron beams arriving in partial areas, for example strips of the structure, are absorbed by the structure, while the electron beam is spread as unimpeded as possible through recesses between the strips. So that appropriately fine line patterns can be mapped, structures are employed which not rarely have distances of less than 500 nm between the strips, wherein the strip widths are often less than 1 xcexcm. Moreover, the structures should not be too thin in order to achieve the necessary image quality, or the required degree of absorption, so that strip heights of 750 nm and more must be attempted.
A method for producing metallic foil masks is described in laid-open DE 1 521 476, wherein the foil masks are initially placed by vapor deposition on a metal matrix and thereafter are again drawn off this matrix. It is known that by the vapor-deposition process it is only possible to produce foil masks of comparatively little thickness within a reasonable amount of time. Customarily, layer thicknesses of 500 nm are not exceeded today, inter alia because of the long deposition times in the vapor-deposition process.
Masks are known from U.S. Pat. No. 5,858,576, the entire contents of which are incorporated herein by reference. Such masks partially include a multi-layered metal structure. But these layers were applied, for example, by an ion focus beam process, which also entails an uneven shape of the strip edges of the mask. Moreover, in the method in accordance with U.S. Pat. No. 5,858,576 all support substrate layers are removed by an etching process. But etching of these support substrate layers, which as a whole are relatively thick, causes etching remnants to remain in the area of the mask, which decides the function, namely between the strips. Because of the fineness of the structures it is hard to remove these remnants and they interfere with the image quality during the subsequent employment of the mask.
Finally, a mask includes several metal layers is disclosed in German Letters Patent DE 23 44 111. Here, a layer of precious metal is applied by galvanization to a support substrate layer. Following galvanization, the two layers are inseparably connected with each other. Because of the process, no filigreed multi-layered structures can be produced in this way, because for reasons of their being manipulable alone, the support substrate layers must already have a sufficient thickness at the start of the process.
An object of the present invention is based on making available a method for producing a self-supporting electron-optical transparent structure, by which it is possible in particular to produce extremely filigreed and accurate patterns. The structures produced in this way differ, inter alia, by their increased fineness and the more even shape of the strip edges.
This object is attained by a method for producing a self-supporting electron-optical transparent structure that includes multi-layer strips and recesses located between the multi-layer strips. The method includes applying a first layer to a second layer, presetting a pattern by exposing or irradiating the first layer and etching the pattern out of the first layer so that partial areas of the second layer are uncovered. The method further includes galvanically applying layers to the uncovered partial areas of the second layer so that multi-layer strips are formed thereon and an electron-optical transparent structure is formed and removing the electron-optical transparent structure off the second layer.
This object is also attained by a self-supporting electron-optical transparent structure that includes multi-layer strips and recesses located between the multi-layer strips. The structure is made by a process that includes applying a first layer to a second layer, presetting a pattern by exposing or irradiating the first layer and etching the pattern out of the first layer so that partial areas of the second layer are uncovered. The method further includes galvanically applying layers to the uncovered partial areas of the second layer so that multi-layer strips are formed thereon and an electron-optical transparent structure is formed and removing the electron-optical transparent structure off the second layer.
The present invention is based on the concept that a fine, multi-layered structure is galvanically applied between border walls to an electrically conductive auxiliary layer, and that the thin structure can be pulled, without being destroyed, off this auxiliary layer. By galvanic application of the layers of the structure it is relatively rapidly and easily possible to obtain layer thicknesses far exceeding 500 nm, so that high-energy electrons can be completely absorbed.
The advantage obtained by the present invention includes making possible the production of extremely filigreed and even self-supporting electron-optical transparent structures.
In accordance with a special embodiment of the present invention, a two-stage etching process is used for bringing out the desired pattern, wherein an electrically conductive layer is used as the etch stop layer. Plasma etching processes are employed in connection with a preferred method variation. Other dry etching or wet etching processes can also be used. For the rest, the term etching not only relates to the dissolution of materials in acids, but also to a corresponding method employing bases.
A galvanic process is understood to be a method wherein layer materials are applied from an ionized state. It is for example possible to electrolytically precipitate metals, such as gold or nickel, out of a preferably aqueous solution to the appropriate surface. Metal ions are discharged and deposited at the cathode. It is possible in the end to build up the desired layer thickness by adjusting the electrical current and the length of the process.
Exemplary embodiments of the present invention will be explained in greater detail by the drawings.